Plant Evolution & Diversity

I. Kingdom Protista: Algae & Protozoa

1. Simple Eukaryotes – mostly single-celled Amoeba, slime molds, euglenoids, algae

2. Organisms in this Kingdom don’t fit clearly into what we call plant, animal, or fungi.

3. Most diverse eukaryotic Kingdom (>60,000 species). 4. We are interested in this Kingdom because of the

Chlorophytes & Charophyceans – green algae.

A. Characteristics

The line between Kingdom Protista and Kingdom Plantae is still being discussed……

Fig 29.4

II. Plant Origins

B. Suspects and Evidence

a. Mostly freshwater, but some are marine.b. Have plant-like chloroplasts.c. There are unicellular and multicellular formsd. Can live symbiotically with fungi as lichens

1. Characteristics of Green Algae - Chlorophytes

Volvox - freshwater

Caulerpa - intertidal

Ulva – sea lettuce

Fig 28.30

2. Characteristics of Green Algae - Charophyceansa. fresh water pondsb. They are considered to be the closest ancestors oftrue plants. Evidence: i. Both have same type of cellulose-synthesizingcomplexes in cell membrane ii. Both have peroxisomes for enzyme storage iii. Both have same type of flagellated sperm iv. Both form a cell plate during cell division v. Genetic evidence – charophyceans share agreater % of similar DNA with true plants than anyother algae

III. Plants Shared CharacteristicsA. Plants are multicellular eukaryotes that arephotosynthetic autotrophs.B. Shared pigmentsC. Cellulose cell wallsD. Store glucose as starchE. Etc.

IV. What challenges did plants face when they “moved” onto land?

A. Issues Faced 1. Acquire, transport, and conserve water 2. Protect from UV radiation 3. Resist pathogens (bacteria) and herbivores (later) 4. Others?

Then why move onto land?B. Advantages 1. 2. 3. 4.

3. Walled spores produced in sporangia

4. Multicellular gametangia

C. Adaptation to life on Land:

1. Apical Meristems

2. Alternation of generations

5. Multicellular, dependent embryos

1. Apical Meristems – localized regions of cell division at tips of roots and shoots

Fig 29.5

2. Alternation of Generations

Fig 29.5

a. 2 multicellular life stages:i. Sporophyte:

* Diploid* Divides by meiosis to form spores* Spores – haploid cells that can grow into anew, multicellular, haploid organism (thegametophyte) without fusing to another cell.

ii. Gametophyte: * Haploid* Divides by mitosis to form the gametes (eggand sperm)

b. Egg & sperm fuse to form the diploid zygote, which divides by mitosis to form the sporophyte

3. Walled spores produced in sporangiaa. Sporopollenin protects the spore from harsh

environmental conditionsb. Sporangia = an organ within the sporophyte that

produces the sporesc. Sporocytes = the diploid cells within the sporangia

that divide by meiosis to form the haploid spores

sporocytes

Fig 29.5

4. Multicellular gametangia

a. Gametangia = multicellular organs within thegametophyte that produce the gametes by mitosis. b. 2 types of gametangia:

i. Archegonia – produce eggs ii. Antheridia – produce sperm

c. Sperm travel to the egg, fertilizing it within thearchegonia.

Fig 29.5

5. Multicelled dependent embryos

a. After fertilization, the zygote remains within the archegonia, gaining nutrients forgrowth from the gametophyte.

b. Zygote divides by mitosis to become thesporophyte.

6. Other examples of adaptations to life on land: (not all plants have the following):

a. Cuticle – waxy covering to prevent desiccation & microbial attackb. Secondary compounds – odors, toxins, tastes, etc. toattract pollinators and defend against herbivoresc. Roots - absorb water and minerals from the soil d. Shoots - stems and leaves to make food. e. Stomata – openings in the leaf surface to allow gas exchange for photosynthesis and to regulate water loss.

f. Lignin in cell walls to provide structural support for Shoots

g. A vascular system that transports food & water fromroots to shoots and vice versa.

V. Plant Phyla

Fig 29.7

A. Nonvascular Land Plants: Bryophyta1. Characteristics a. Earliest land plants b. Phyla: Hepatophyta – liverworts,Anthocerophyta – hornworts, and Bryophyta –mosses c. Inhabit most environments, including extremes d. Peat moss (Sphagnum): doesn’t decay rapidly, stores 400 billion tons of carbon e. Gametophyte is the dominant generation f. No true roots nor leaves

2. Moss Life Cycle

Fig 29.8

a. Hepatophyta – liverworts3. Bryophyta Phyla

b. Anthocerophyta – hornworts

c. Bryophyta - mosses

d. Sphagnum moss (stores carbon, doesn’t decay, fuel source) Peat bogs

Fig 29.10

B. Vascular Plants 1. Characteristics a. Vascular tissue Xylem = water & mineral

transport and Phloem = food (carbohydrates) transport b. Dominant generation = sporophyte c. Sporophytes branched, independent of gametophyte

parentd. Leaves = Micorphylls to Megaphyllse. Root development

2. Groups

Tiny gametophytes living just above or below soil surfaceEgg & Sperm need moist environment to fertilize (similar to bryophytes)

a. Seedless Vascular Plantsi. Characteristics

Microphyll leaves

b. Two phyla of seedless vascular plants:

i. Phylum Lycophyta (Club Mosses) They diverged first from bryophytes with an unbranched

vascular system, flammable spore clouds, and were tree-like in the Carboniferous (late Paleozoic) period

ii. Phylum PterophytaWhisk ferns – no true leaves or rootsHorsetails – hollow air-filled stems (adaptation to water-

logged,low O2 environment)Ferns – produce clusters (sori) of sporangia on underside of leaves (fronds)

Phylum Lycophyta: club mosses, spike mosses, quill warts

Phylum Pterophyta: ferns, horsetails, whisk ferns

Fig 29.12

c. Fern Life Cycle

d. Factors forest changes of the Carboniferous period (290 to 360 mya)

i. Lycophytes (tree-like) & Pteridophytes ii. First forestsiii. Swampy forests – slow decay in low O2, formed deep layers of organic matter iv. Heat + pressure + time => coal v. Pulled lots of CO2 out of atmosphere, cooling theearth & forming glaciers vi. Larger species died out when climate became drier

3. Terrestrial Adaptations of Seed Plants a. Seeds replace spores as main means of dispersal.

i. Why? ii. More resistant to harsh environ b/c multicellulariii. old way (ferns & mosses): spores released fromsporangia to disperse and develop into gametophytes iv. new way: the sporophyte RETAINS its spores within the sporangia & the tiny gametophytedevelops within the spore.

v. ovule = female sporangium + female spore. Female gametophyte develops within the spore &produces eggs. vi. after fertilization, the ovule becomes the seedvii. seed = sporophyte embryo + food supply (matureovule tissues)

Similar to Fig 30.2

b. Reduction of the gametophyte:

i. Old way: sporangia spores bisexual gametophyte (antheridia sperm, archegonia eggs)ii. New way:Megasporangia megaspores female gametophyte eggsMicrosporangia microspores male gametophyte sperm

c. Heterospory – separate male & female gametophytes

d. Ovules and seed production i. Megasporangia protected by layers of tissuecalled integuments. ii. Ovule = integuments, megasporangia, & megasporeiii. Megaspore female gametophyte egg &food supplyiv. After fertilization, embryo develops, ovule becomes a seed

Fig 30.3

e. Pollen & Pollination i. Microsporangia microspores male gametophyte sperm ii. Pollen = male gametophyteiii. Pollination = transfer of pollen to ovule by windor animalsiv. Pollen tube brings sperm to egg within the ovule

4. Two types of seed plants: a. Gymnosperms i. Characteristics Evolved first and “Naked seed” – seeds develop on surface of specialized leaves called sporophylls

ii. Four phyla:Ginkophyta – only Ginko bilobaCycadophyta – Cycads (look like palms)Gnetophyta – Gnetophytes (tropical trees)Coniferophyta – Conifers – cone-bearing trees

Dominate forests of the N. hemisphereMost are evergreenNeedle-shaped Megaphyll leaves to reduce water

loss during drought

Phylum Cycadophyta

Phylum Ginkophyta

Phylum Gnetophyta

Phylum Coniferophyta

Fig 30.6

iii. Gymnosperm Life Cycle

b. Angiosperms i. CharacteristicsFlowering plants, Most diverse, and Evolved from gymnosperms: Sporophylls rolled together to form ovaries. ii. One phylum: AnthophytaSeeds are enclosed in the moist reproductive tissue of thesporophyte generation (Ovary).More insects and animals for pollination, less dependenton wind.Formerly only 2 classes: monocots & dicots. Now 4clades (evolutionary lines):

Basal angiosperms, Magnoliads, Monocots, & Eudicots

iii. Evolutionary success of AngiospermsIncreased water transport efficiency due toimprovement in xylem tissue: tracheid cells, fibercells, vessel elements (gymnosperms only havetracheids)Flowers – attract pollinatorsFruits – many forms for variety of dispersalmechanisms

Fig 30.3iv. Angiosperm Life Cycle

Notice the triploid stage!Each pollen grain (male gametophyte) produces two spermSperm travel down the pollen tube & into the ovule.Double fertilization – one sperm unites with the egg to form the 2n zygote, other sperm unites with the two nuclei of the female gametophyte to form a 3n endosperm – becomes food for the developing embryoOvule matures into the seed – contains sporophyte embryo & endosperm (food).Ovary (female sporangium tissues) matures into the fruit.

Fig 29.8

Moss Life Cycle

Fig 29.12

Fern Life Cycle

Fig 30.6

Gymnosperm Life Cycle

Fig 30.3Angiosperm Life Cycle

VI. Kingdom Fungi

Fungi were once included in the plant kingdom becausethey produce spores, have cell walls, and are notanimals.

A. Characteristics1. Their cell walls do not contain cellulose (like plants),

but do contain chitin (like insects, arthropods).2. Their bodies are filamentous.

3. The organization of large structures such as mushrooms and morels is completely different from plants. 4. They are heterotrophs (acquire nutrients by absorption).

B. Fungal life cycle

C. Ecological Roles of Fungi:1. Decomposers – absorb nutrients from deadorganic matter, thereby decomposing it. Recyclenutrients to the soil.

2. Parasites – absorb nutrients from living hosts. ex. pathogens on crops

3. Mutualists with plants – absorb nutrients from host, butaid host in mineral uptake from soil. ex. mycorrhizae

1. Molds: rapid growing, asexually reproducing fungi2. Yeasts: single-celled fungi inhabiting moist habitats. Raise bread & ferment alcohol

D. Lifestyles of Fungi

3. Lichens: symbiotic association of cyanobacteria or green algae and fungi. a. Fungus provides shape and attachment b. Algae provides food, N to the fungus c. Lichens are very sensitive to air pollution; used as indicators of air quality.

4. Mycorrhizae: mutualistic association of plant roots and fungi. a. Fungus increases the absorptive surface area of roots, increasing water and potassium uptakeb. Fungus receives food from the root exudates.